A review of analogue model studies of the coast effect

1981

In order to ease the interpretation of geomagnetic data for resource charting and tectonic studies of the Queen Charlotte Islands region, the behaviour of the electromagnetic variations over the region is studied using a laboratory analogue model. The results indicate that conductive channelling is important in Hecate Strait for both E and H source field polarizations. Current deflection is observed at Rose Point for E-Polarization and at the northern and southern tips of the Queen Charlotte Islands for H-Polarization. Model results for simulated variations of 4, 40, and 120min show a wide range of field values over the Queen Charlotte Islands, for example, HZ varies by a factor of 4 or more between coastal and inland locations for E-Polarization at short periods and by as much as a factor of 5 between certain coastal locations at long periods. The model results show that in decreasing the depth of the conducting layer in the mantle from 200 to 100km, the Hz, Hx, Ex, and EY anomalies are attenuated by 20%, and the Hy anomalies by roughly 8% over the deep ocean and by 12% over Hecate Strait for 4min period variations.

Section: Model Descriptionmentioning

confidence: 99%

Section: Model Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

An analogue model study of electromagnetic induction in the Queen Charlotte Islands region.

Chan

1981

“…The laboratory modelling facility, described previously by Dosso (1966Dosso ( , 1973 to a depth of 0.63m with saturated salt solution. The measuring system has also been described previously and will not be repeated here.…”

Section: Analogue Model Descriptionmentioning

confidence: 99%

The electromagnetic response of the Assistance Bay region.

Heard

et al. 1983

The electromagnetic response of the Assistance Bay region (N.W.T., Canada) is studied using laboratory analogue model and field station measurements. Magnetic field components for the frequency range 0.1-15Hz, which includes the well known lightning induced Schumann Resonances, were measured at 8 sites along a 6 km line through the central region of Assistance Bay and roughly perpendicular to the Cornwallis Island coastline. Two of the stations were on land and six were off-shore on the ice. Although the field data were examined in the three bandwidths 0.1-6Hz, 6-10Hz, and 10-15Hz, the present work deals only with the 8Hz Schumann Resonance component within the 6-10Hz range. Calculated average amplitudes and phases of the three magnetic field components show the relative response of the region at stations along the 6km line. The response is discussed in terms of the effect of the on shore topography, the coastline, and the bathymetry.A laboratory analogue model of the Assistance Bay region was constructed and model measurements carried out for a simulated frequency of 8 Hz for E-Polarization (electric field in the east-west direction) and H -Polarization (electric field in the north-south direction) of an overhead uniform horizontal inducing field. The magnetic field amplitudes Hx, Hy, Hz for both polarizations for 10 traverses perpendicular to the coastline are presented and the anomalous fields attributed to the response of the coastline bay, capes, bathymetry and source field polarization.The analogue model and the field station coast effects (vertical to horizontal field ratio) are compared for the model traverse coinciding with the 6km line of field stations. The analogue model results show a maximum enhancement of approximately 1.3 directly over the coastline with rapidly decreasing values seaward followed by a second enhancement over the sharp ocean depth gradient beyond the 55 m depth contour. The field station results do not show maximum at the coastline, but rather an increasing value seaward, reaching a value of 1.7 at the station over the sharp ocean depth gradient near the 55 m depth contour, indicating the effective coastline to be at the deep water edge. This difference may in part be attributed to the shallow water conductivity being smaller than simulated in the laboratory model. The effect of the 2m layer of ice, as well as the accumulation of fresh water from streams in the Assistance Bay region, may lead to a significantly lower effective conductivity than assumed for the

“…The laboratory analogue model, the measuring equipment, the source field and end effects have all been described previously (Dosso, 1966(Dosso, , 1973CHAN et al, 1981a) of 15kHz and 90kHz simulate geomagnetic variations with periods of 30 min. and 5 min.…”

mentioning

confidence: 99%

Laboratory model magnetic fields for the Hainan Island region.

1983

The behaviour of the electromagnetic fields over the Hainan Island region of the South China Sea is studied using a scaled laboratory analogue model. The model source frequencies used simulate periods of 5 min. to 30 min. in the geophysical scale. To examine the electromagnetic field variations due to the irregular coastlines, the deep ocean, a narrow ocean channel, and an atoll (modelled as a seamount), field components for individual traverses over the model are presented.The coast effect for the bay coastline is visible only for short periods at which the depth of the bay is at least .1 skin depths. The response of the seamount, overlain by a 500m depth ocean, differs greatly from the response of an island. Electric current flow over the seamount, confined to this thin layer, produces a quadrature field directly opposite to that for an island. Buried features such as the seamount and depth profile of the deep ocean show the largest in-phase response at the lower frequency where the overlying ocean is much less than .1 skin depth thick.